The synthesis of metal perfluoro alkyl phthalocyanines has been the subject of several disclosures by the inventor S. M. Gorun. Their ability to catalyze oxidations by activating dioxygen chemically in homogeneous solutions, for example for thiols oxidation to disulfide (See US Patent Publication No. 20150315137 to Gorun et al. and incorporated by reference herein) or photochemically in homogeneous solutions or within a polymer matrix have been well documented in the art (See US Patent Publication No. 20150284592 to Gorun et al. and incorporated by reference herein). This ability depends to a large degree on the availability of the metal center for coordination by oxygen and/or reagents, a function that is usually possible due to (i) the kinetic lability of the solvents in which the phthalocyanine is dissolved, and (ii) the absence of a solvent when the phthalocyanines are embedded in a polymer matrix. In other words, in solution the solvents bind weakly or not at all to the metal center. While homogeneous catalysis a valuable process, constructing heterogeneous catalysts that can be easily separated from reactants and products, for example via filtration, or used in solid-gas processes remains a valuable goal for materials science. Heterogenizing a homogeneous catalyst by attaching it to a solid-state support, while desirable does not guarantee retention of reactivity. Phthalocyanine (Pc) materials are conjugated macrocycles known in the art to be chemically or photochemically active. In particular, fluoro alkylated fluoro phthalocyanines are known to exhibit useful aerobic catalytic properties.
With respect to homogeneous vs. heterogeneous catalysis, it is known that unsubstituted phthalocyanines, PcM, where M can be a metal or non-metal, are used as pigments. They exhibit very low solubility in organic solvents. However, as described previously, the introduction of substituents at the periphery of the macrocycle enhances the PcM solubility, bulky substituents being particularly effective due to their ability to prevent intermolecular phthalocyanine π-π aggregation, one of the leading causes of insolubility. Peripheral substituents, however, are required to enhance or reduce the electronic density of the phthalocyanine macrocycles, as required by a particular catalytic process or desired property. While beneficial for homogeneous catalysis, the presence of Pc substituents hinders the use of PcM alone as heterogeneous materials. Depositing phthalocyanines on supports is known in the art, the aim being to prevent their leaching in solution and thus maintaining the heterogeneous nature of a process in which the said phthalocyanine/support participates.
A homogenous catalyst, as stated above, is problematic when it comes to separate it from the useful products into which it is mixed. U.S. Pat. No. 6,511,971 to S. M. Gorun (entitled “Substituted perhalogenated phthalocyanines”) and US Patent Publication No. 2015368194 to Gorun et al entitled “System and Method for Fluoralkylated Fluorophthalocyanines with Aggregating Properties and Catalytic Driven Pathway for Oxidizing Thiols,” both of which are incorporated by reference herein, describe fluorinated phthalocyanines that are able to bind and activate oxygen in solution. Metal fluorophthalocyanines are capable of forming reactive oxygen species, either via transfer of accumulated photochemical energy to oxygen, or via the transmission electrons provided by other species, for example thiolate anions. The attachment of fluorinated phthalocyanines to a support, for example SiO2 or TiO2, is also known to yield active materials, but they do not function in organic solvents since the phthalocyanines leach out. DeSisto et al, Industrial & Engineering Chemistry Research, 47, 7857 (2008), describe imidazole-functionalized mesoporous silica gel beads that absorb selectively nitric oxide (NO), when a cobalt phthalocyanines substituted with four sulfonic acid interacts with the mesoporous silica. The absorption is essentially irreversible (a single turnover), a process that is inconsistent with a catalytic process that, by definition requires multiple turnovers. Owens et al, Inorganica Chimica Acta, 277, 1 (1998) confirms the instability in non-aqueous solvents of the silica-imidazole phthalocyanine adducts as well as binding of NO. The application envisioned is denitrification.
Folkesson et al, J. Appl. Electrochem. 13, 355 (1983) describes electrodes that contain a polymeric phthalocyanine catalyst fixed to an activated carbon carrier by a covalent link of imidazole. The lifetime of the electrode is limited probably due to the splitting of the carbon-imidazole nitrogen bond linking the imidazole to the surface.
The replacement of C—H bonds by C—F bonds, both aromatic and/or aliphatic has resulted in the formation of the phthalocyanine scaffolds of FIG. 1, including the compounds with Rf═C3F7 (perfluoro isopropyl) and Rf═R′, scaffold, as well as R═H2N, scaffold 2. Both scaffolds may accommodate a variety of metal centers, for example, Zn(II), Co(II), Mg(II), Cu(II), Fe(II), Ru(II), Pt(II), Pd(II), Al(III), Ga(III), In(III), V(IV), etc., as the steric ability of the 4 central N to coordinate metal centers is not sterically hindered by the Rf, R′ ring substituents.
US Patent Publication No. 2013064712 A1 and WO 2011045029 to Roeder et al., describe scaffold 1 complexes that are supported on SiO2, but they remain attached only in the absence of organic solvents. EP19850301973, to Sumitomo teaches the removal of polycyclic aromatic with supported phthalocyanines. The links to the solid-state support are established by covalently bonding the phthalocyanines through any one of various bivalent groups, with a reactive group, such as dihalotriazine, monohalotriazine, trihalopyrimidine, sulfato ethylsulfone, etc.
Considering the above facts, there is a need in the art for catalytic materials that are insoluble in organic solvents and thereby act as heterogeneous oxidation catalysts in such media, with the advantages thereof.